1. Field of the Invention:
The present invention relates generally to cotton harvesters and, more specifically, to an improved doffer for doffing cotton from picker spindles.
2. Related Art:
In the mechanical harvesting of cotton with spindle-type picking units, such as exemplified by the John Deere Model 9960 Cotton Picker, rotating spindles project into the row-receiving area of a harvester row unit to remove cotton from the plant. The rotating spindles are then moved under the face of a doffer of the type exemplified in U.S. Pat. No. 4,644,736, Cerney et al, of common ownership with the present invention. The tangential velocity of the doffer is significantly greater than that of the spindle, and the motion of the doffer relative to the spindle unwraps cotton from the spindle, strips the cotton off the end of the spindle, and propels the cotton into a conveying air stream.
A conventional doffer has radially configured straight-edged lugs molded into the working face of the doffer disc to facilitate the doffing action. The action of the radially configured lugs provides a large stripping force component and a relatively small unwrapping force component. As a result of the distribution of force components, unwrapped cotton is frequently forced between the spindle and the doffer. As the wrapped spindles are forced through the doffer, the leading or working edges of the lugs wear, and the lugs flex. Doffer wear and chunking out of pieces of the lugs because of the lug flexure results in significantly reduced doffer life and need for frequent doffer adjustment. To prevent failure due to wrapped spindle induced flexure stress, doffers must be made of a more supple material; however, such a material typically does not have the wear resistance of a harder material so that wear is sacrificed for chunking resistance.
The radial lugs also have an instantaneous point of contact with the spindles at the outer leading edges of the lugs, and the remainder of the lug edge backs off from the spindle as the doffer rotates. As a result, the outer leading edges of the lug wear faster than the radially inward portions. Doffer pads often have to be replaced before the inner portions of the leading edges are worn significantly.
Propelling the cotton doffed from the spindles into the conveying air stream is an important function of the rotating doffer. Since the angle of contact between the spindle and leading edge of a radial doffer lug varies as the spindle passes through the doffing zone, the trajectory from the doffer is diffused. Also the distance of trajectory is relatively short because of the inefficient unwrapping action of the radial lug.
Present doffer lug configuration also requires that the spindles remain in the doffing zone a relatively long period of time for proper doffing. As a result, the cam and cam follower arrangement that orients the bars of spindles is subject to heavy loading and wear in the doffing zone.
The doffing action of the doffers frequently results in twists in the lint of the cotton boll (known as "prep"). Presence of prep lowers the grade of cotton and results in a lower prices for the farmer.
Doffing action of presently available doffers limits the range of crop conditions over which satisfactory picker operation can be achieved. In marginal conditions, less than optimal doffer efficiency can make the difference between being able to pick and not being able to pick.